The invention concerns a procedure for the production of structured parts with cavities consisting of plastics, cellulose or wood granulate, in particular of light-weight construction compound parts, using molding tools. Gas-creating insertion elements are also used in the procedure.
The European patent EP 0 478 535 [B1] already contains a description of plastic-coated parts such as pressure pads and rolls, whereas a further layer for the reduction or removal of adhesion is applied between the part and the epoxy coating in a locally limited procedure. To create cavities in the layer, the layer is filled with fluids or gas, through which the epoxy coating will arch outwards. Consequently, the surrounding area of a roll can be deformed in a desired manner depending on order and size of the cavities.
The German patent application DE 33 24 705 A1 describes a procedure for the production of a sound-absorbing lining with cavities which is made of textiles; this lining is preferably used for the construction of vehicles in order to line sound-sensible fields on the one hand and protect against airborne sound on the other hand. The lining consists of at least two mats that are made of textiles, for example reprocessed wool, that have been fabricated with a binding agent at raised temperature. A plastic part, i.e. a continuous tape, is inserted between the mats. The individual layers are then shed with needles and pressed together. In certain areas, the mats and the continuous tape will be pressed more strongly than in others. During the pressing procedure, the plastic part will melt or create gas at the processing temperature; as a consequence, cavities are created in the areas with smaller compression. The areas with higher compression serve as bindings to stiffen the mats. Furthermore, the mats will be combined area by area by binding agents which become effective under the heat and thus the mat will be bound. The plastic parts are preferably made of polystyrol foam, e.g. of thermoformable plastics or other epoxies with low melting temperature.
The composite material described in the European patent application EP 0 679 501 A1 is particularly known for its use in the production of sealing materials in automobile technology which are used for sealing cavities. This composite material consists of a cavity forming supporting material which again contains a xe2x80x9chot-foamingxe2x80x9d material. Hot-foaming means that such a material (e.g. polymerics or copolymers of ethylene and unsaturated acrylic esters) will transform at least partly when they are heating up. The temperature of the supporting material, e.g. with polyamide plastic components, is higher than the temperature at the beginning of the foaming process. The composite material is always fabricated in pre-selected forms; afterwards the form will be placed in an installation site designed for the sealing process. For this procedure, the supporting material has to have at least one, preferably two oppositely arranged apertures, through which the foaming material will exit after the activation; the foam will consequently seal the composite material with the walls. An example for the production procedure of composite material parts would be the extrusion of hot-foaming material between two polyamid foils. The composite material parts are then punched into the pre-selected form, thus combining the two external structures.
The support material will not deform during the production process, it will only lead the foam leaking out through the cavities towards the sealing areas.
Furthermore, there is a process for reaction plastics injection molding as described in the German Disclosure DE-OS 1 926 688 which has been developed for the production of a mold part with a dense outer layer made of a polyurethane thermoset. The tool parts are used in automobile technology and household appliance industry, where big-size high-quality tool parts with thick cross sections required. The reaction plastics injection molding of foaming polyurethane thermoset takes place in a mold with core parts. The core is formed by an elastic wrapper with a cylinder-shaped opening and is filled with a gas or a liquid.
As described in the European Patent Application EP 0 443 364 A2, there is a laminated plastic which consists of stable fixings in a foaming or honeycomb core layer made of a temperature-resistant epoxy. In the core layer, foaming inserts that have a higher density than the core layer are placed near the fixing places. The core layer is coated with at least one layer of a fiber-reinforced temperature-resistant epoxy. Such laminated plastics are preferably used for the construction of interior parts for airplanes. An example for the incorporation of the inserts into the core layer would be the shaping of hollows into the core layer, and inserting a granular material blowing agent. The foaming granular material enters into the core layer and anchors there. Self-cutting tapped bushings can then be screwed into the insert. The blowing agents are used for foaming an epoxy in order to create a foam with high density.
The U.S. Pat. No. 4,113,909 also specifies the production of hexagonal structures of a plastomer to be used in light-weight building boards. A plate of the thermoplast is inserted between two molding boards, then heated up; afterwards the boards are drawn apart. Hereby the thermoplast form, now in heated condition, sticks to the molding boards and the drawn-apart thermoplast material forms a honeycomb structure.
The present invention aims at developing a procedure to manufacture particularly light, but at the same time solid, molding tools, in particular of light-weight construction compound parts.
This goal can be achieved through a procedure for manufacturing structured parts with cavities consisting of plastics, cellulose or wood granulate, in particular to form light-weight compound parts making use of tool parts following the features submitted under claim 1.
The said procedure for the production of structured parts with cavities made of plastics, cellulose or wood granulate using tool parts allows an expansion of the matrix material by inserting pre-shaped gas-creating substances in the matrix material at pre-selected places, and subsequently activating the insertion elements in the tool parts to produce gas, thus creating light-weight macro-cavities, which are preferably filled only with gas and the residue of the blowing agent and not with heavy foam.
The present invention extends the state of the art by offering the possibility to create several, but separately structured macro-cavities inside a matrix material without external gas conduction, which will preferably lead to a honeycomb structure formation with a homogeneous combination with the surface layers.
The said insertion elements which consist of gas-creating substances and a surrounding or solid coating, will be applicated to fiber webs in the form of circular, polygon or ring-shaped discs and implemented as single parts between at least two of the pre-fabricated layers of plastic, wood, or granulated material in double-sided films; these pre-fabricated layers are then inserted into the mold and subsequently coated by injection molding or extrusion or pressing to a homogeneous compound ready to be triggered for gas creation on the implemented inserts for lift-off in order to create the hollow structure.
A further possibility for the stationary fixing of the insertion elements would be the use of textile inserts. During the weaving process, the weaving machine pointedly places the insertion elements in the programmed pattern.
Multiple-staged weaving machines will insert the gas-creating substances in the said offset pattern in two layers. The prefabricated weavings with the included insertion elements positioned in the mold and the left cavity of the mold are filled by injected plastics. The subsequent creation of gas causes a tension of the reinforcement until the yielding point is reached. Due to the reinforcement, the compound part will be of greater solidity.
The submitted procedure makes it possible to coat light-weight structures with cavities in an economic process by inserting foils or a decor film inside the mold surfaces. These light-weight construction compound parts have a high specific strength-weight relation and are especially suited for cladding, covers and crash-proof parts in car, ship and airborne vehicle design. Using reinforced sheets of plastics or sheet steels as surface layers, high-strength structural parts are set up. In addition to good sound and heat insulation through the cavities, the thickness of the structure walls can be held small. Three-dimensionally shaped hulls that are homogeneously bound with the matrix on the surface layers form a stable compound; furthermore, the cavities can be used to implement hollow elements including pipes and cables as single-double corrugated structures.
The presented invention differs from existing hot-foaming processes and foaming material inside hollow structures by the following features:
The local situation of the cavities is predetermined by the situation of the insertion elements.
The cavity size lies in the macro-area and is predetermined by the size of the insertion elements.
The structured compound from the thin-walled encirclement of the cavities by the matrix material, as well as the combination of the bordering surface layer consists of a supporting homogenously bound matrix material.
The design of the thickness of the matrix material walls, the form and size of the cavities, are predetermined by form and situation and the amount of blowing agent; and are arranged according to static requirements.
The structured compound is arranged according to the direction of the form of the insertion elements and their size in accordance to the loads of the part.
The gasification and therefore the creation of cavities will preferably occur in a predetermined manner and in locally limited areas. The blowing agent substances will be activated after the local thermoplastic deformation of the pre-form and hot tack adhesion of layers or pre-formed layers in order to create the macro-cavities e.g. for a light-weight compound, web systems, isolation cavities etc.
The method for the punctual ignition of the gas-creating process of insertion elements imbedded in a matrix material of plastics, cellulose or wood granulate will preferably be applied according to the following features:
Exothermic Processes:
Transgression of a certain pressure which is necessary for gasification,
by injecting (molding) additional matrix material,
by pressing and compressing a form,
Transgression of a certain temperature which is necessary for gasification,
by external additional warming such as radiation or convection,
by rubbing the particles by means of pressure or shifting,
by the friction of films and the resulting contact friction energy, microwave radiation, ultrasound, energetic radiation from outside;
Endothermic Processes:
the mechanical mixing of gas- or heat-creating components using external pressure or shifting,
thermal melting of substances coated by protective layers with gas or heat-creating substances with at least two components resulting in a subsequent reaction,
the bursting of covers of included substances and their resulting reaction, the diffusion of two gas-creating substances which are separated by a porous film which, for the ignition/activation, will penetrate the film and then react
Time-delayed Processes:
chemical reaction with determined delay,
attaining a certain mass by compression in order to trigger the gas- or heat-creating reaction;
triggering the reaction by placing additives of endotherm processing material
Combination of the previously mentioned processes.
The processes of exothermic gasification are preferably combined by creating heat within the matrix material layer. The exothermic reaction softens the matrix material during the thermoforming of the matrix material. The endothermic gasification is combined with a temperature reduction which can then be used for the rapid hardening of the thermoplastics. The advantage of an endothermic gas-creating substance lies in the controlled process of gasification and the shorter cycle periods.
In addition, physical gases consisting of easily evaporating hydrocarbons (pentene to heptane KP 30 to 100xc2x0 C.) can be used for the procedure. Chemical exothermic Azo-combinations, N-nitroso-combinations and sulfonyl-hydracides can also be employed at kick-off temperatures from 90 to 275xc2x0 C. Suitable chemical endothermic (temperature raising) agents are NaHCO3 and Hydrocerol. The previously mentioned substances generally start decomposing as soon as they reach a certain kick-off temperature, which corresponds to the requirements for the matrix materials, thereby creating gas. The widely-used azo-dicarbonamid can be adjusted to starting temperatures of 155-200xc2x0 C. by so-called kick-offs, for example Pb- and Sn stabilizers.
The blowing agent substances are produced as powders or granular materials. They will be added to the hopper of an injection molding machine as a granular material or, for epoxy components, as liquid additives (powder). During the extruding, injection molding, and pressing processes, the gasification process is laid off by the high injection pressure.
Moreover, gas-creating insertion elements can be inserted which consist of heat-resistant explosives that release the prescribed amount of gas through electric ignition. This method is presently used for airbags in the automobile industry. For the complete explosive transition, insensitive explosives (blasting agents) require effective ignition agents (celluloseulose nitrate, Hg-fulminate, plumbum acid, argentum acid, tetracene, nitrophenol (diaodine nitrophenol), plumbum nitroresorcinate) or boosters (e.g.: glycerine nitrate, glycol di-nitrate, ammonium nitrate).
For the usage the processes of GFK, CFK, RFC, wood pulp or celluloseulose as porous and viscose matrix material, the gasification can happen within film blisters or airbag/mattress-like welded double films optionally; thus, a light-weight compound with a waver structure or honeycomb structures or an egg-crate shaped inner layer can be created.